A selective reduction NOx catalyst (hereinafter, SCR) and an occlusion reduction NOx catalyst (hereinafter, LNT), for example, are well known as a post-processing device that reduces and purifies nitrogen compounds (hereinafter, NOx) contained in exhaust gas discharged from a diesel engine (internal combustion engine).
In the SCR, the NOx in the exhaust gas can be reduced and purified by promoting the reductive reaction of the NOx with ammonia (NH3) that is supplied as a reduction agent. In the LNT, the NOx in the exhaust gas is occluded when an air-fuel ratio of the exhaust gas is lean. On the other hand, when the air-fuel ratio is raised by unburned fuel (HC) that is supplied as the reduction agent, the LNT discharges the occluded NOx such that the NOx is reduced and purified by CO, HC, H2, and so on in the exhaust gas.
For the purpose of supplying ammonia or unburned fuel to the post-processing device as the reduction agent, a reduction agent supply means is provided on an exhaust pipe at the upstream side of the post-processing device.
However, space of a vehicle body wherein the exhaust gas purification device being provided is limited. For this reason, a patent document 1, for example, discloses an exhaust gas purification device comprising a first connecting section for turning the direction of the exhaust gas discharged from a diesel particulate filter, a linear section being jointed to the first connecting section in the form of L-shaped and having provided on the upstream end thereof the reduction agent supply means, and a second connecting section being jointed to the linear section in the form of L-shaped and having provided on the downstream end thereof the SCR catalyst device, wherein the reduction agent being injected and mixed with swirl flow in the exhaust pipe so that the reduction agent can efficiently be supplied to the SCR catalyst device.